The present invention is directed to a tamperproof cap assembly. In particular, the invention is directed to a cap assembly which may be used in combination with a hydrant having a valve stem rod which is operated to open and close the hydrant valve either by displacement of the valve stem rod in elevation without rotation of the valve stem rod about its axis or by rotation of the valve stem rod.
A hydrant having an operating mechanism for displacing the valve stem without rotating the stem is described in detail in U.S. Pat. No. 4,062,375 for "Tamperproof Lock" assigned to the assignee herein. The tamperproof cap assembly of the present invention is especially intended for use with such a hyrant.
Various tamperproof cap assemblies have been proposed heretofore. Such assemblies are, in general, unduly complex in structure and are not readily adapted for use with subsisting hydrants.
For example, in U.S. Pat. No. 468,782 for "Fire Hydrant," there is disclosed a cap which is hinged to the hydrant nozzle. The hydrant is provided with a casing having a projection which abuts the lug portion of the cap when the cap is closed on the hydrant nozzle. A curved bolt locks the lug portion to the projection. The valve stem rod is provided with an eccentric which is splined to the valve stem rod. Rotation of the valve stem rod causes the eccentric to displace a linkage thereby releasing the bolt to free the cap. Vertical displacement of the valve stem rod does not affect the operation of the eccentric. Accordingly, the rather complicated mechanism described in this patent is unsuitable for use with a hydrant having a valve stem rod which is displaceable in elevation but which is not rotatable about its axis.
Various other cap assemblies are described in U.S. Pat. Nos. 3,914,996 for "Protection Device And Tool For Fire Hydrant" and 556,500 for "Hydrant."